html5 canvas 使用示例

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代码如下:

<!DOCTYPE HTML>
<html>
<head>
<meta charset="UTF-8">
<title>HTML5示例</title>
<style type="text/css">
#container{border:1px solid #ccc;width:800px;height:600px;position:relative;}
canvas{position:absolute;top:0px;left:0px;z-index:1;}
</style>
</head>
<body>
<select id="tools">
<option value="pen">铅笔</option>
<option value="line">直线</option>
<option value="rect">矩形</option>
<option value="circle">圆形</option>
<option value="ellipse">椭圆</option>
</select>
<div id="container">
<canvas id="canvas" width="800" height="600"></canvas>
<canvas id="canvas_temp" style="z-index:2;" width="800" height="600"></canvas>
</div>
<script type="text/javascript">
var canvas = document.getElementById('canvas');
var context = canvas.getContext('2d');

var _canvas = document.getElementById('canvas_temp');
var _context = _canvas.getContext('2d');
var tools= document.getElementById('tools');

tools.onchange = function (e){
tool[this.value]();
};
var tool = {
pen:function (){
this.reset();
_canvas.onmousedown=function (e){
_context.moveTo(e.layerX,e.layerY);
_canvas.onmousemove=function (e){
_context.lineTo(e.layerX,e.layerY);
_context.stroke();
};
_canvas.onmouseup=function (e){
_canvas.onmousemove=null;
_canvas.onmouseup=null;
tool.updata();
};
};
},
line:function (){
this.reset();
_canvas.onmousedown=function (e){
var _e = e;
_canvas.onmousemove=function (e){
_context.clearRect(0,0,canvas.width,canvas.height);
_context.beginPath();
_context.moveTo(_e.layerX,_e.layerY);
_context.lineTo(e.layerX,e.layerY);
_context.stroke();
_context.closePath();
};
_canvas.onmouseup=function (e){
_canvas.onmousemove=null;
_canvas.onmouseup=null;
tool.updata();
};
}
},
rect:function (){
this.reset();
_canvas.onmousedown=function (e){
var _e = e;
_context.strokeStyle="#000";
_canvas.onmousemove=function (e){
_context.clearRect(0,0,canvas.width,canvas.height);
_context.strokeRect(_e.layerX,_e.layerY,e.layerX-_e.layerX,e.layerY-_e.layerY);
};
_canvas.onmouseup=function (e){
_canvas.onmousemove=null;
_canvas.onmouseup=null;
tool.updata();
};
}
},
circle:function (){
this.reset();
_canvas.onmousedown=function (e){
var _e = e;
_canvas.onmousemove=function (e){
_context.clearRect(0,0,canvas.width,canvas.height);
_context.beginPath();
_context.arc(_e.layerX,_e.layerY,e.layerX-_e.layerX,0,Math.PI*2,true);
_context.stroke();
_context.closePath();
};
_canvas.onmouseup=function (e){
_canvas.onmousemove=null;
_canvas.onmouseup=null;
tool.updata();
};
}
},
ellipse:function (){
this.reset();
_canvas.onmousedown=function (e){
var _e = e;
_canvas.onmousemove=function (e){
var st=0;
_context.clearRect(0,0,canvas.width,canvas.height);
_context.beginPath();
_context.moveTo(_e.layerX+(e.layerX-_e.layerX)*Math.cos(st), _e.layerY+(e.layerX-_e.layerX)*Math.sin(st));
st+=1/180*Math.PI;
for(var i=0;i<360;i++){
_context.lineTo(_e.layerX+(e.layerX-_e.layerX)*Math.cos(st),_e.layerY+(e.layerY-_e.layerY)*Math.sin(st));
st+=1/180*Math.PI;
}
_context.stroke();
_context.closePath();
};
_canvas.onmouseup=function (e){
_canvas.onmousemove=null;
_canvas.onmouseup=null;
tool.updata();
};
}
},
reset:function (){
_canvas.onmousedown=null;
_canvas.onmouseup=null;
_canvas.onmousemove=null;
},
updata:function (){
context.drawImage(_canvas, 0, 0);
_context.clearRect(0, 0, canvas.width, canvas.height);
}
};
tool['pen']();
</script>
</body>
</html>